When preparing my universal app for iTunes I was having trouble with getting the icon.png file the right size. When I saved a 57×57 pixel icon iTunes complained about needing a 72×72 pixel icon for the iPad an vice versa for the iPhone. So I googled and found there are a couple of things you need to do.

STEP 1

Create all the icons listed in here under Table 3: Universal apps icon requirements. Then add them to your project in xcode. (you know, drag em into your resources folder)

http://developer.apple.com/library/ios/#qa/qa1686/_index.html

STEP 2

On that same page down the bottom are the instructions for how to enter these to your info.plist. Follow them, or just add this to your info.plist if it isn’t in there already. (I prefer to edit the info.plist myself in textEdit) If you are using a cocos project, especially 0.99.5 or newer, it should already be in there.